In recent years, the semiconductor industry has widely adopted copper or copper-containing compounds as conductive materials and low dielectric constant (low-k) materials as insulating materials for interconnection between transistors in integrated circuit (IC) manufacturing. One manufacturing step that helps ensure the successful integration of copper and low-k dielectric materials is the deposition of barrier materials between copper and dielectric materials. The barrier materials may also be called diffusion barrier or liner materials. Barrier materials may serve both as a diffusion barrier that prevents the diffusion or migration of the conductive materials into the insulating materials and active regions of transistors, and as an adhesion promoter that eliminates delamination and voids between the conductive materials and the surrounding regions of insulating, dielectric materials.
Materials that are suitable for use as barrier materials generally possess one or more of the following qualities: strong mechanical and structural integrity, high electrical conductivity, good conformal coverage over device features, and high chemical, mechanical, and electrical stability against defect formation. Furthermore, barrier materials should have one or more of the aforementioned qualities at increasingly reduced thickness. For example, a typical barrier layer thickness may be 20 nm for a 150 nm device.
Barrier materials have evolved from transition metals such as, tantalum and tungsten, to transition metal binary compounds such as, for example, tantalum nitride (TaNx) and tungsten nitride (WNx). More recently, transition metal ternary compounds such as tungsten-nitride-carbide (WNxCy), tantalum-silicon-nitride (TaSixNy), and tungsten-silicon-nitride (WSixNy) have been considered for use as a barrier material. In this connection, one such material, tungsten-nitride-carbide (WNxCy), may be suitable for use as a barrier material in deep sub-100 nm IC devices because it is a highly refractory material with high mechanical and chemical stability even at elevated temperatures. The incorporation of carbon into these barrier materials greatly enhances the chemical and mechanical stabilities of the barrier film so that a much thinner film (<5 nm) is adequate as the copper diffusion barrier.
Transition metal ternary compound thin films are typically deposited from chemical precursors that are reacted in a processing chamber to form films in a chemical vapor deposition (CVD) process such as metal-organic chemical vapor deposition (MOCVD). As the barrier layer thickness further decreases, these barrier materials may be deposited onto semiconductor substrates (wafers) by atomic layer deposition (ALD) or atomic layer chemical vapor deposition processes (ALCVD) in which the films are deposited in controlled, nearly monoatomic layers. A high quality thin barrier film of tungsten nitride carbide can be deposited, for example, by ALD through a pulsed exposure sequence of NH3 (ammonia), B(C2H5)3 (triethyl boron), and WF6 (tungsten hexafluoride) at one or more temperatures ranging from 300 to 350° C. An example of an ALD deposition of a WNxCy film is provided, for example, in the reference Wei-Min Li et al., “Deposition of WNxCy thin films by ALCVD method for diffusion barriers in metallization”, Proceedings of the 5th IEEE International Interconnect Technology Conference, Burlingame, Calif.
While the deposition process desirably forms barrier films on a substrate (typically a silicon wafer), the reactions that form these films also occur non-productively on other exposed surfaces inside of the processing chamber. Accumulation of deposition residues results in particle shedding, degradation of deposition uniformity, and processing drifts. These effects can lead to wafer defects and subsequent device failure. Therefore, periodic cleaning of the processing chambers, also referred to as chamber cleaning, is necessary. CVD chambers used for deposition of tungsten (W) metal films and binary tungsten compounds such as tungsten silicide are typically cleaned with fluorine-containing plasmas. In these cleaning processes, atomic fluorine can react with tungsten and silicon to form volatile byproducts such as, for example, WFm(m=1-6) and SiFn(n=1-4). The volatile byproducts are then removed from the chamber by vacuum pump.
While there is a large body of work on etching tungsten metal, and dry cleaning of conventional CVD chambers used for depositing tungsten metal and other dielectric materials such as SiO2, these applications and processes are not directly applicable to transition metal ternary compounds such as tungsten-nitride-carbide (WNxCy) because these materials are much more chemically stable and highly refractory. Furthermore, the incorporation of carbon into certain transition metal ternary materials poses additional challenges. Unlike tungsten and silicon, the carbon component in a thin film or deposition residue does not typically form volatile byproducts with fluorine atoms. Instead, the carbon component tends to form nonvolatile fluorocarbon polymer residues. As tungsten and/or silicon components are removed as volatile byproducts, the remaining residues become carbon enriched. Such a problem has become well known in etching and cleaning of carbon-doped silicate glass (CSG) low dielectric constant materials. In the case of tungsten carbide (WC), fluorine-containing plasmas preferentially remove the tungsten component and leave the carbon particles behind.
CVD and/or ALD chambers used for tungsten carbide and tungsten depositions have to be periodically disassembled and cleaned by mechanical means (scrubbing or blasting) and/or by wet chemical solutions. A mixture of potassium ferricyanide (K3Fe(CN)6), sodium hydroxide (NaOH), and water (H2O) has been found to effectively remove WC coatings. Mechanical and wet clean processes are time consuming and labor intensive.
Accordingly, the IC industry needs a viable dry chamber cleaning technology that can reliably remove the deposition residues of transition metal ternary compounds. Compared with wet or mechanical cleaning, dry chamber cleaning preserves process chamber vacuum. Compared with disassembling the process chamber followed by wet or mechanical cleaning, a dry cleaning technology can greatly minimize chamber down time, and hence increase wafer throughput.